Gaseous electric discharge devices



Nov. 25, 1958 J. R. ACTON ET AL GASEOUS ELECTRIC DISCHARGE DEVICES Filed March 22, 1956 IN VEN TORS ATTORNEY United States Patent C "'ce 2,862,133

Patented Nov. 25, 1958 GASEOUS ELECTRIC DISCHARGE DEVICES John Reginald Acton and Kenneth Harold Westley, Beeston, England, assignors to Ericsson Telephones Limited, London, England Application March 22, 1956, Serial No. 573,200 Claims priority, application Great Britain March 22, 1955 Claims. (Cl. 313-178) The present invention relates to gaseous electric discharge devices of the type having, within a sealed envelope, at least two electrodes, namely a cold cathode and an anode. A trigger electrode by means of which a discharge between the cathode and anode can be initiated is usually also provided. Examples of such devices are trigger triodes and indicator tubes.

It is the principal object of the present invention to provide a device of the type specified which is simpler in design and cheaper to produce than known devices of the same character.

The invention is based upon the following considerations. It is necessary to provide a getter to clean up residual traces of oxygen and if the getter is carried in a suitable container, and the getter itself is suitably chosen, the container can advantageously form a substantial part of the cathode of the device. Moreover if the getter is suitably chosen, the production of a high degree of vacuum before introducing the gas-filling is unnecessary with a considerable having in cost of pro duction.

According to the present invention, therefore, a discharge device of the type specified comprises a getter capsule electrically connected to the cathode, the capsule comprising a container in which the getter is carried during manufacture and which is of a material that is less volatile than the getter, the getter having a work function of about 3.5 electron volts or less and being adapted to extract residual oxygen from the envelope, and the container being so disposed that, in operation, its surface constitutes at least 5% of the whole surface of the cathode which forms one terminal of the discharge.

The getter is preferably a substance such as barium which has a low work function and whose work function is decreased, or at least not greatly increased by combi nation with oxygen.

According to the present invention in another aspect, in a discharge device of the type specified the cathode is constituted by a wire projecting into the envelope and having fixed near to its end a getter capsule, the capsule comprising a hollow container which is of a material that is less volatile than the getter, and the getter having a work function of about 3.5 electron volts or less and being adapted to extract residual oxygen from the envelope.

The cathodes that are normally used in discharge devices of the type specified have an inherently long life. However an important factor in determining the life of a discharge tube having a cathode constituted in accord ance with the present invention, is the nature of the gasfilling. If this is of relatively high atomic weight, such as argon or neon for example, the life is found to be considerably reduced by bombardment of the cathode by heavy ions. Where the emission of light is not of significance, therefore, that is in all cases other than indicator tubes and the like, the use of gases of relatively high atomic weight should, therefore, be avoided.

According to a subsidiary feature of the invention,

therefore, when the discharge device is one, such as a trigger triode, in which the emission of light is not a material consideration, the gas-filling consists of helium, or substantially helium, gases having a greater atomic weight than helium constituting not more than 2% and preferably not more than 1% of the filling.

The invention also provides a method of making a discharge device of the type specified comprising the steps of inserting at least two wires into the mouth of a vitreous tube, one of the wires forming an anode lead and one or more of the wires forming connecting means to the cathode and supporting a getter capsule in the form of a container having within it a getter which is more volatile than the material of the container, which can combine with residual oxygen, and which has a work function of about 3.5 or less, and an electrically-conductive member forming with the container a closed loop, locating the wires relatively to one another at a region close to but outside the vitreous tube, heating the mouth of the tube and forming a pinch in which the wires are sealed, pumping the tube to a pressure not below 0.002 mm. of mercury, admitting a gas filling, sealing off the tube and volatilising the getter by induction of current in the closed loop.

The gas pressure may be between 20 and 600 mm. of mercury. In the case of a small trigger tube a filling of helium at about mm. of mercury is suitable.

The invention will be described by way of example with reference to the accompanying drawing in which:

Fig. 1 shows a stage in the manufacture of a triode according to the invention.

Fig. 2 shows a further stage in the manufacture of the triode of Fig. 1,

Figs. 3 and 4 are enlarged views in front and side elevation of the cathode in Figs. 1 and 2,

Fig. 5 shows electrodes of another embodiment of the invention assembled on a base,

Fig. 6 shows a modified form of cathode that may be used in the invention,

Fig. 7 shows, in section, an indicator tube according to the invention.

Fig. 8 shows a modified form of cathode for use in an indicator tube such as is shown in Fig. 7, and

Fig. 9 shows a double-ended tube according to the invention.

Referring to Figs. 1 and 2, a glass tube 10 which may be about 8 mm. in internal diameter and about 28 mm. long is open at one end and from its other end extends a pumping tube 11 of smaller diameter. Into the mouth of this tube are inserted three nickel wires 12, 13 and 14 welded respectively to copper wires 15 which extend outwards through the mouth.

To the inner end of the nickel wire 12 is welded a nickel wire 16 bent into U-shape with the limbs of the U projecting away from and parallel to the wire and about 3 mm. apart. A tube 17 of iron or other relatively nonvolatile material (such as copper or nickel) containing barium which has a work function of about 2.2 electron volts, is welded between the two arms of the U as best shown in Figs. 3 and 4. The three wires 12,, 13.,and 14 are supported in a suitable clamp 18 (Fig. 2) close, to but outside the glass tube at appropriate spacings, with the plane of the U perpendicular to a line passing through the three wires. The mouth of the tube is then heated and the pinch is formed at 19 in Fig. 2, the ends of the copper wires adjacent the nickel wires sealing into the glass. The tube is heated by suitable gas jets and crudely evacuated through the pumping tube 11, say to a pressure of 0.005 mm. of mercury. Helium is then admitted through the pumping tube 11 and the latter is sealed off. The pressure of the helium may be 130 mm. of mercury. The overall length of the finished tube is about 30 mm. The getter is then flashed by inductive heating of the loop comprising the U-shaped wire 16 and the getter tube 17, the barium volatilising and condensing upon adjacent surfaces including the U--shaped wire, the nickel wire =supporting'the U-shaped wireand the outside of the getter-containing tube 17. At the same time residual oxygen in the tube is taken up with the formation of barium oxide which also has a low work func tion.

Inoperation, the cathode, "that is to say the terminal of the glow discharge, is constituted by the whole of the nickel wire projecting from the pinch 12, the U- shaped n'ickel wire 16, and the tube "17 that originally contained the getter, the last-named tube having a superficial area which in this example is about of the total superficial area of the cathode. The wire 13 constitutes the trigger electrode and may have a gap of about'0l3 mm. between it and the cathode 16, 17. The wire '14 constitutes the anode and may be spaced at about 6mm. from the cathode. The tube described will operate .to switch a current of about 2 to 6 milliamps.

The getter tube is preferably hermetically sealed with the barium within it since it can then be handled without difficulty. It may be formed in known manner as shown in Fig. 4 with a flat 20 ground thereon, thereby providing a region of weakness along the tube at which when flashing takes place the tube can readily burst.

The tube described is-of extremely simple construction embodying a small number of parts and requiring for its manufacture a small number of welds. These features with the avoidance of the need for a high vacuum make the tube cheap to produce. The production described can, of course, be carried out using a suitable conveyor carrying a number of tubes each passing successively through a number of work stations'at each of which a different operation is performed.

Fig. 5 shows an electrode assembly for a diode-triode for use in the dark, that is to say in the absence of photons. -In this example the cathode comprises a U- shaped member 21 supported upon two nickel wires 22 and 23 and carrying two getter tubes 24 and 25, each as described with reference to Figs. 3 and 4. The trigger electrode is shown at 26, spaced at about 0.3 mm. from the cathode, and the anode at 27 spaced at about 8 mm. from the cathode. A light anode and cathode 28 and 29 having a gap at 30 of about 0.4 mm. between them provide a permanent source of ionised particles when a suitable potential difference is maintained between them. In this example the electrodes are mounted upon a standard7-pin glass base 32. The base 32 is sealed into an envelope and a filling of helium at 85 mm. of mercury is provided in the manner described with reference to Figs. 1 to -4. An additional electrode 31 is provided in this example and may be used for any desired purpose.

A modification of the diode-triode of Fig. 5 has a cathode as shown in Fig. 6. It comprises a U-shaped support21 mounted on two wires 22 and 23 and carrying three'getter tubes 33 and three nickel bars '34 to increase the cathode area. The barium deposits upon the whole surface of the cathode when the getter is flashed. A filling 'of'he'lium at 100 mm. of mercury is used in this example with a trigger to cathode spacing of about 0.3 mmpand an anode to cathode spacing of about 11 mm.

Fig. 7 shows an indicator tube having only two electrodes, namely a cathode 35 and an anode 36, these electrodes having the same form as the electrodes 12, 16, 17 and 14 in Figs. 1 to 4. They are mounted within a glass envelope 37 and in this case the filling is of 99.5% neon and 0.5% argon at a pressure of mm. of mercury.

When a very 'small tube is required, the U-sh'aped member of the cathode may be bent as shown in Fig. 8, which has the same references as Figs. 3 and 4, in .such a manner as to bring the two arms of the U 16 closer together.

In order that the indicating tube, which of necessity contains heavier gases, since it is required to emit light, may have a reasonably long life, the operating current should be kept low; for example about 0.2 milliamp.

Fig. 9 shows a double-ended tube which is a modification of that in Fig. 5, like parts having the same reference in the two figures. The cathode is as shown in Figs. 3 and 4. In this example the anode 27 and light anode and cathode 28 and 29 are atone end of the tube and the main cathode 16, 17 and trigger electrode 26 are at the opposite endof the tube. The trigger to cathode spacing is about 0.3 mm. and the anode to cathode spacing about 5 mm. A filling of helium at mm. of mercury is used.

We claim:

1. A gaseous discharge device comprising -a sealed envelope and within the envelope a cathode, and an anode, said cathode comprising a getter container whose surface constitutes at least .5% of the surface of said cathode, and saidenvelope having a gas filling at least 98% of which is helium.

2. A method of making a gaseous discharge device comprising the steps of supporting in fixed relation to one-another at least two wires one to'constitute an anode and at least one to formpart of a cathode and supporting a getter capsulecontaining a getter which is more volatile than the material of the container, which can combine with residual oxygen, and which has a work function of about 3.5 or less, inserting the said wires into the mouth of a vitreous tube, sealing the wires in the said mouth, pumping the tube to a pressure not below trodes and a getter within an envelope, pumping said envelope to a pressure not below 0.002 mm. of mercury, admitting helium to said envelope, sealing off said envelope, and thereafter volatilising said :getter.

References Citedin the file of this .patent UNITED STATES PATENTS 2,680,206 Rich June 1, .1954 2,682,619 Landrey June 29, 1954 FOREIGN PATENTS 716,621 Great Britain Oct. 13, 1954 

1. A GASEOUS DISCHARGE DEVICE COMPRISING A SEALED ENVELOPE AND WITHIN THE ENVELOPE A CATHODE, AND AN ANODE, SAID CATHODE COMPRISING A GETTER CONTAINER WHOSE SURFACE CONSTITUTES AT LEAST 5% OF THE SURFACE OF SAID CATHODE, AND SAID EVENLOPE HAVING A GAS FILLING AT LEAST 98% OF WHICH IS HELIUM. 